1. Field of the Invention
This invention generally relates to semiconductor manufacturing equipment and, more particularly, to an apparatus and method used for rapid thermal processing of a single semiconductor wafer.
2. Description of Related Art
In the semiconductor industry, to continue to make advancements in the development of semiconductor devices, especially semiconductor devices of decreased dimensions, new processing and manufacturing techniques have been developed. One such processing technique is know as Rapid Thermal Processing (RTP), which reduces the amount of time that a semiconductor device is exposed to high temperatures during processing. The RTP technique, typically includes irradiating the semiconductor device or wafer with sufficient power to quickly raise the temperature of the wafer and hold it at that temperature for a time long enough to successfully perform a fabrication process, but which avoids such problems as unwanted dopant diffusion that would otherwise occur at the high processing temperatures. Generally, RTP uses a light source and reflectors to heat the wafer. In a conventional rapid thermal processor a lamp is used as the light source because of its low thermal mass, which makes it easy to power up and down very quickly.
Unfortunately, conventional lamp-based RTP systems have considerable drawbacks with regard to uniform temperature distribution. Any single variation in the power output from the lamps can adversely affect the temperature distribution across the wafer. Because most lamp-based systems use lamps with filaments, the wafer is usually rotated to ensure that the temperature non-uniformity due to the filament array is not transferred to the wafer during exposure. The moving parts used to rotate the wafer, add to the cost and complexity of the system. Another particularly troublesome area for maintaining uniform temperature distribution is at the outer edges of the wafer. Most conventional RTP systems have no adequate means to adjust for this type of temperature non-uniformity. As a result, transient temperature fluctuations occur which may cause slip dislocations in the wafer at high temperatures (e.g. .about.1000.degree. C.).
Conventional lamp-based RTP systems have other drawbacks. For example, there are no adequate means for providing uniform power distribution and temperature uniformity during transient periods, such as when the lamps are powered on and off. Repeatability of performance is also usually a drawback of lamp-based systems, since each lamp tends to perform differently as it ages. Replacing lamps can also be costly and time consuming, especially when one considers that a given lamp system may have upwards of 180 lamps. The power requirement of the system may also be costly, since the lamps may have a peak power consumption of about 250 kWatts.
For the above reasons, what is needed is an apparatus and method for isothermally distributing a temperature across the surface of a semiconductor device during rapid thermal processing.